The present invention relates to an improved printed circuit board apparatus, and in particular to an improved face plate assembly for varying kinds of printed circuit boards which are to be mounted in a rack housing.
It is common in the telecommunications field to have rack housings which are intended to accommodate a plurality of printed circuit board assemblies therein, each assembly being mounted in the rack housing by sliding it inward so as to be parallel and closely adjacent to other printed circuit boards. Each circuit board has a plurality of electrical pins extending from its back end which commonly engage a like plurality of housing pin contacts, and through these pins and contacts signals pass so that integrated circuits and other electronic elements on the printed circuit boards can send and receive signals to and from other electronic components either situated within the particular rack housing in question or other electronic components electrically connected to the pin contacts of the rack housing.
Presently available printed circuit board assemblies suffer from a plurality of disadvantages. First, numerous printed circuit boards used in the telecommunications industry in particular are deemed to perform critical functions, and as such at least one redundant board is generally provided for each critical board so that in the event one of these critical boards fails the telecommunications system served by the critical board automatically switches over to the redundant board and thereafter utilizes the redundant board to perform operations required thereby so that system failure is prevented. With such critical boards, it is common to provide a manual switch on a face plate of the critical board which can be toggled prior to removing the critical board for inspection or other required work. Upon toggling of the switch, the critical board, which is in its active mode, is disabled and replaced by the redundant board in what is commonly known as a graceful transition by electronics associated with the telecommunications system. Such graceful transitions generally are made at a convenient processing time for microprocessors associated with the telecommunications system, for example at the end of an information frame or superframe, as opposed to instantaneously within the middle of a frame and possibly even in the middle of a packet or byte contained in the frame. Commonly, numerous graceful transition instants occur each second. A disadvantage with such face plates is that oftentimes a craftsperson forgets to activate the switch prior to removing an active critical board whereby the telecommunications system is forced to enter its failure switching mode which, if occurring at an inconvenient instant, can result in lost data, lost data cycling efficiency, and false system alarms.
Printed circuit board assemblies also have to guard against electrostatic discharges which can be caused by static electricity associated with a board being inserted into a rack housing and/or static electricity on a craftsperson handling the board when inserting it into a rack housing. A common construction for guarding against electrostatic discharge is to provide an elongated grounding pin at the back of the printed circuit board which makes contact with the rack housing prior to any signaling pins associated with the printed circuit board, with the elongated pin thereby discharging any undesired electrostatic charges present to ground via the rack housing. This design solution is relatively expensive.
Finally, any rack housing which accommodates several boards, such as 10-20 boards or more, necessarily houses boards having different functions and boards which require different user interfaces such as varying unique arrangement of lights on a face plate thereof for communicating information to a craftsperson such as power ON, power OFF, unique component failures, etc. Individually machining each face plate to accommodate its unique user interface design tends to be inefficient and costly.